886
FXUS21 KWNC 092005
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST December 09 2025

SYNOPSIS: Mid-level low pressure over eastern Alaska downstream from a strong
mid-level high pressure ridge centered west of the Alaska Mainland are forecast
to bring very cold air and dangerous wind chills across central and southern
Alaska, along with episodes of high winds across southern Alaska from the
Aleutians into Southeast Alaska. Enhanced onshore flow into the northwestern
contiguous U.S. (CONUS) is forecast to persist from week-1 well into week-2
with mid-level low and high pressure to the north and south of the region,
respectively. An Arctic air mass is forecast to move south of the Canadian
border into the north-central CONUS, before progressing rapidly eastward across
the Great Lakes and Northeast. For much of the East however, increased return
flow from the Gulf is expected to moderate temperatures.

HAZARDS

Moderate risk of high winds across southern Alaska from the eastern Aleutians
through central Southeast Alaska, Wed-Sat, Dec 17-20.

Slight risk of high winds for southern Alaska from the central Aleutians
through Southeast Alaska, Wed-Tue, Dec 17-23.

Moderate risk of much below normal temperatures for Southeast Alaska and the
Copper River Basin, Wed-Fri, Dec 17-19.

Slight risk of much below normal temperatures for much of central, eastern, and
southern Alaska, Wed-Sun, Dec 17-21.

Moderate risk of heavy precipitation for the Pacific Northwest and northwestern
California, Wed-Sat, Dec 17-20.

Slight risk of heavy precipitation for the Pacific Northwest and northwestern
California as far south as San Francisco Bay, Wed-Tue, Dec 17-23.

Moderate risk of heavy snow across the Northern and Central Cascades, Wed-Sat,
Dec 17-20.

Slight risk of heavy snow across the Cascades, Klamath, and Northern and
Central Sierra Nevada Ranges, Wed-Tue, Dec 17-23.

Slight risk of heavy snow across part of the northern Rockies and adjacent High
Plains, Wed-Tue, Dec 17-23.

Moderate risk of high winds for portions of the Pacific Northwest and
northwestern California, Wed-Sat, Dec 17-20.

Slight risk of high winds from the Pacific Northwest and Northern California
(as far south as San Francisco Bay) eastward into the Northern Rockies,
Wed-Tue, Dec 17-23.

Slight risk of much below normal temperatures for the Upper Mississippi Valley
and western Great Lakes region, Thu-Sat, Dec 18-20.

Slight risk of high winds from the Great Lakes region to the Atlantic coast
from Maine southward to the Delmarva Peninsula, Wed-Sun, Dec 17-21.

Flooding possible across parts of the Pacific Northwest.

DETAILED SUMMARY

FOR FRIDAY DECEMBER 12 - TUESDAY DECEMBER 16:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR WEDNESDAY DECEMBER 17 - TUESDAY DECEMBER 23: The 0z ECWMF, GEFS, and
Canadian ensembles depict an amplified mid-level ridge centered west of Alaska,
with an amplified downstream mid-level trough established over eastern Alaska.
At the surface, this set-up favors persistent high pressure across much of
Alaska and the Yukon throughout week-2. Conversely, mean low pressure is
favored in the Gulf of Alaska. The pressure gradient between these features
brings increased chances for episodes of high winds across much of southern
Alaska between the central Aleutian Islands through much of Southeast Alaska.
High winds would be particularly favored in gaps and inlets. Probabilistic
Extremes Tools (PETs) show enhanced chances of wind speeds exceeding the 85th
climatological percentile. Therefore, a slight risk of high winds (for all of
week-2) and a moderate risk of high winds (valid Dec 17-20) are posted for most
of southern Alaska.



PETs continue to highlight enhanced chances for temperatures to fall to near
hazardous thresholds across portions of south-central, Interior, and Southeast
Alaska. As the Bering Sea ridge continues to retrograde and weaken, the
anomalous cold (and associated northerly flow) will gradually expand westward
across the state. A moderate risk is posted for Southeast Alaska, including the
Copper River Basin, for Dec 17-19, while a broader slight risk is maintained
for much of the Interior, south-central, and Southeast Alaska for most of
week-2. Temperatures between -20 deg F and -30 deg F are predicted to be
widespread across much of inland Alaska, with -40 deg F temperatures indicated
by the PETs over the eastern Interior to the north of Fairbanks. Closer to the
coast, temperatures are expected to range between 0 and -15 deg F. The
combination of very cold weather and high winds along the southern tier of the
state increases the threat for heavy freezing spray at times near larger bodies
of water.



The 0z ECENS and 0z CMCE model solutions predict a mid-level ridge will extend
from off the California coast east-northeastward into the Four Corners region
coincident with a mid-level trough over eastern Alaska. The 0z GEFS, however,
predicts a more amplified ridge along the West Coast, which displaces the
Pacific jet stream and mean storm track farther north than the other solutions.
This creates significant uncertainty regarding the forecast location of the
storm track, increased onshore flow, and associated heavy precipitation, with
the GEFS favoring northwestern Oregon and Washington, and the ECENS and CMCE
favoring Washington southward across Northern California. This discrepancy is
depicted clearly in both the PETs and the IVT guidance. The ECENS precipitation
guidance is more robust compared to the GEFS counterparts, with a widespread
area of 2 inches favored across much of the Pacific Northwest and the coast of
at least Northern California, with uncertainty in how far south this feature
may extend into Central California. Leaning a bit more towards the ECENS and
CMCE solutions, a moderate risk of heavy precipitation is posted for western
portions of Washington and Oregon, and the northwestern tip of California, Dec
17-20, with a slight risk area that continues south to near the San Francisco
Bay area, Dec 17-23. As this moisture streams farther inland, heavy mountain
snow is expected to fall across the Cascades, Klamath, and Northern and Central
Sierra Ranges. A moderate risk of heavy snow is posted based on the
uncalibrated ECENS tool indicating elevated chances for snowfall exceeding a
foot for the Northern and Central Cascades, Dec 17-20. A broader slight risk
area designated from the Northern Cascades to the Central Sierras, along with a
separate slight risk for heavy snow is also posted for the vicinity of the
Northern Rockies, both valid for Dec 17-23.  An increased pressure gradient
across the Pacific Northwest and Northern California (resulting from high
pressure predicted to the south and low pressure to the north) warrants a
moderate risk of high winds for the Pacific Northwest and northwestern
California, Dec 17-20, and a slight risk of high winds continuing south to near
San Francisco, Dec 17-23. PETs indicate wind speeds in excess of the 85th
climatological percentile and at least 20-25 mph. These wind speeds will be
reassessed tomorrow, along with the increasing potential for a significant
atmospheric river beginning later in week-1 and continuing through most, if not
all, of week-2. Finally, a flooding possible hazard remains posted for portions
of western Washington and northern Oregon, where any additional precipitation
may increase the risk for flooding and landslides (especially in areas of steep
terrain) as the soil conditions will remain wet from an atmospheric river in
week-1.



Temperatures across the East are expected to moderate as the week-2 period
progresses, coincident with a predicted rapid flattening of the 500-hPa flow
pattern and the migration of surface high pressure off the Southeast coast.
This favors increasing return flow from the Gulf of America, with non-hazardous
precipitation overspreading much of the Lower Mississippi and Tennessee Valleys
early in the period. In early week-2, a shallow undercutting Arctic air mass is
depicted by the models to rapidly progress south of the Canadian border into
the Dakotas, Upper Mississippi Valley, and western Great Lakes region.
Thereafter, this air mass is predicted to be escorted rapidly eastward across
the remainder of the Great Lakes and the Northeast by fast westerlies, with
little additional southward penetration. Accordingly, a slight risk of much
below-normal temperatures is indicated over the vicinity of the Upper
Mississippi Valley and western Great Lakes region, Dec 18-20. The uncalibrated
GEFS and ECENS tools briefly support wind chill values near -20 deg F in this
area. Finally, enhanced wind speeds are favored from the Lakes region eastward
to the Atlantic coast from Maine southward to the Delmarva Peninsula, with PETs
predicting speeds exceeding the 85th climatological percentile and 20-25 mph.
This is related to low pressure passing north of the Great Lakes during the
first and middle portions of the forecast period, and surface high pressure
centered over/near the Tennessee Valley.

FORECASTER: Anthony Artusa

$$